1. Field of the Invention
The invention relates to an electric clock, particularly a quartz-crystal controlled clock, having an electric motor, especially a single-phase stepping motor, with a permanent-magnet rotor whose shaft is supported at each end of the shaft and at one end protrudes into a damping chamber filled with a damping liquid.
2. Description of the Prior Art
In electric clocks, especially in quartz clocks, an almost noiseless running of the clock is frequently required. The fulfillment of this requirement is particularly difficult in clocks with a stepping motor. A relatively high noise level prevails in such clocks because of the jerky advance of the rotor and the overswing occurring at the end of each rotor step, which interacts with the play between the individual gears of the hand mechanism driven by the motor.
It is already known to place one end of the motor shaft in a damping chamber filled with a damping liquid in order to lower the noise level. Thus the noise level can be considerably lowered. However, since damping liquids of a comparatively low viscosity must be used because of the generally small starting torque of the stepping motors which are usually employed, considerable difficulties occur in the packing of the damping chamber at the entrance of the shaft. Tests with customary packing agents have hitherto not led to a satisfactory result. In a discharge-proof packing, the friction occurring between packing and shaft would be too great, and in a packing with small frictional forces acting upon the shaft, it would not be possible safely to prevent a discharge of the damping liquid.